1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a copying machine or a facsimile machine using an electro-photographic system or an electrostatic recording system. More particularly, the present invention relates to an image forming apparatus having a rotary brush for applying lubricant to the surface of an image carrier. The present invention also relates to a cleaning unit for cleaning the surface of the image carrier in the image forming apparatus.
2. Description of the Related Art
FIG. 6 of the accompanying drawings schematically illustrates a known image forming apparatus of the type under consideration. Referring to FIG. 6, it is adapted to clean the surface of the image carrier (photosensitive drum) 15 of the apparatus by means of a cleaning unit 18 each time after transferring an image. More specifically, the residual toner on the surface of the image carrier 15 is scraped off by means of a cleaning blade 42 and, at the same time, a rotary brush 51 arranged upstream relative to the cleaning blade 42 in the sense of revolution of the image carrier 15 is brought into contact with solid lubricant 53 and driven to revolve in the sense of revolution indicated by an arrow in FIG. 6 at a rotary speed greater than that of the image carrier 15 to apply lubricant with a reduced contact resistance on the part of the cleaning blade 42. The toner adhering to the rotary brush 51 is removed by a flicker 54 and collected by a toner transporting auger 60.
Another known image forming apparatus uses a cleaning unit that is different from the above described one and adapted to fit solid lubricant to a support panel, guide the support panel by means of a brush cover and causes the support panel to contact with a rotary brush by its own weight (see, inter alia, Patent Document 1 listed below).
Still another known image forming apparatus uses a cleaning unit that is different from the above described ones and adapted to utilize a lubricant roller as solid lubricant and cause it to revolve and contact with a rotary brush (see, inter alia, Patent Document 2 listed below).
[Patent Document 1]
Japanese Patent Application Laid-Open Publication No. 7-210051 (page 1, FIG. 1)
[Patent Document 2]
Japanese Patent Application Laid-Open Publication No. 2001-51561 (page 1, FIG. 1)
However, the technique of FIG. 6 (and that of Patent Document 1) is accompanied by a problem as described below. The solid lubricant 53 can vibrate randomly in the axial direction of the rotary brush 51 and/or vertically as the rotary brush 51 is driven to revolve. Then, the rate of consumption of solid lubricant 53 will not uniform and can vary depending on the winding direction of the bristles of the rotary brush 51 so that, as time goes by, the cross section of left end part a of the solid lubricant 53 can become different from that of the right end part b thereof as shown in FIG. 7. As a result, solid lubricant 53 will be made to adhere to the rotary brush 51 at a varying rate. As solid lubricant 53 adheres to the rotary brush 51 at a varying rate, it is applied to the image carrier 15 also at a varying rate so that consequently the contact resistance of the cleaning blade 42 becomes uneven relative to the image carrier 15 in its axial direction. Then, the edge of the cleaning blade 42 can be worn unevenly and become nicked. Such a cleaning blade 42 can no longer effectively remove the residual toner on the image carrier 15 and clean its surface.
As the effect of cleaning the surface of the image carrier 15 becomes uneven, the film thickness of the image carrier 15 also becomes uneven as shown in FIG. 8. More specifically, in the illustrated instance, the film thickness of the image carrier 15 is reduced only slightly to a small extent w1 (and hence the film thickness t1 is large) at the part of the image carrier 15 that corresponds to the part of the solid lubricant 53 showing cross section 53a, whereas the film thickness of the image carrier 15 is reduced to a large extent w2 (and hence the film thickness t2 is small) at the part of the image carrier 15 that corresponds to the part of the solid lubricant 53 showing cross section 53b. As the image carrier 15 is worn unevenly in this way, the density of the image formed by means of the image carrier 15 also becomes uneven.
On the other hand, with the technique of Patent Document 2, a lubricant roller is driven to revolve and contact with a rotary brush. In other words, both the lubricant roller and the rotary brush require a mechanism for driving them to revolve so that the overall structure of the image forming apparatus becomes a complicated one. Additionally, the lubricant needs to be moved toward the rotary brush as the former is consumed and becomes slim. Then, the solid lubricant comes to be accompanied by the above identified problem of showing a cross section that varies between the left and right ends thereof as in the case of FIG. 6 and Patent Document 1.